The present invention relates to a vehicular headlamp employing a semiconductor light-emitting element such as a light-emitting diode as a light source and which has an improved light distribution.
An incandescent bulb or a discharge bulb has often been used as a light source of a vehicular headlamp. However, recently attention has been given to a light-emitting element such as a light-emitting diode (LED) for use as a light source of a vehicular headlamp so as to achieve lower power consumption and a more compact size.
Vehicular lamps other than headlamps using LEDs include high-mount stop lamps, rear side marker lamps, and the like.
When a semiconductor type light-emitting element such as a LED is used as a light source of a vehicular headlamp, it is necessary to employ different optical design techniques than in the case of an incandescent or discharge bulb in order to obtain the desired light distribution pattern for the low beam of the headlamp. For example, in a lamp employing for its light source a large number of semiconductor light sources arranged in a matrix configuration, switching may be employed to select from among multiple optical functions. (See, for example, Japanese Laid-Open Patent Application No. 2001-266620, FIGS. 1 and 4.)
When an LED is used having a rotationally symmetric light output with respect to the optical axis, precise optical design of the reflecting surface of the lamp's reflector or of lens steps in the front lens is required in order to obtain a light distribution, such as that needed for a headlamp, that is not rotationally symmetric. For designing lamps using semiconductor light-emitting elements, a method is known whereby modeling of the internal structure of the semiconductor element is performed, and the form of the lens steps is modified based on simulation results of light ray tracing or light distribution. (See, for example, Japanese Laid-Open Patent Application No. 7-225790, FIG. 11.)
However, there is a problem concerning the formation of a desired headlamp light distribution since the pattern of light emitted by a conventional light-emitting system has a substantially circular shape when viewed in the direction of the optical axis. For example, in the case of low-beam light, it is difficult to obtain a clear cut line (or cut-off line) that defines a constant boundary.